Hollowtech Chainset Question

[fausto99]

plenty of HT-II cranksets use an aluminium spindle. In the photos it looks more like an aluminium spindle than a steel one, but photos are deceptive which is why I asked. If it is steel it will be thin walled, go rusty where the plating wears off, and a magnet will stick to it. Aluminium ones go black where they corrode, then get worn smooth where they move around. They are thicker walled and a magnet won't stick.

Strictly speaking what you see there arguably cannot be 'fretting' because this wear mechanism relies upon micro-welding between metals. A tightly fitting plastic sleeve cannot fret, not to start with. It can cause crevice corrosion, it can wear via abrasive wear, there are many possibilities, but not fretting per se.

cheers

Definitively steel. I can tell by looking and feeling the real thing rather than the photos and yes, magnets do stick to it. Memo to self; must use more grease.

[tim-b]

Hi

Loose corrosion substances n contact would be whats vibrating, If there was no water and no deposits the bearing parts and the shaft would sit happily together.

Thanks, so am I right to think that noticeable play in the crankset isn't necessary for this type of damage?
Regards
tim-b

[Brucey]

damage of that sort can start as corrosion, but once it has occurred, the dimensions of the fitting parts are likely to be such that some movement will always occur in any further service (and cause further damage) unless you do something about it, as per my earlier post.

The amount of movement required to cause further damage is really very small; a few tens of microns is enough. To assess whether you have a bad clearance is quite difficult; one simple method that works reasonably well is to poke the BB spindle into the LH cup from the left side, and see if the plastic top hat is still a snug fit on the spindle in the 'worn' area or not. Looking at the photos, I'd say most likely 'not' even with a new set of BB bearings/top hats.

BTW the term 'fretting' has a highly specific meaning and it is widely misused.

cheers

[Kojak]

Hi
Thanks, so am I right to think that noticeable play in the crankset isn't necessary for this type of damage?
Regards
tim-b

Correct, your issue is not necessarily down to this type of corrosion but as Brucey says, once damage (whatever the cause) is there and you have 'play' that will get worse so I suppose you could end up with issues like yours. But i'm a bit out of my depth with knock on effects on a bike.

[MikeDee]

Aren't the bearings supposed to spin with (not on) the shaft? I'd say replace the bearings.


I'm a trendy consumer. Just look at my wobbly bog brush using hovercraft full of eels Pro

[Brucey]

the bearings can be absolutely fine but if the spindle isn't a tight fit up the middle of them it will move vs the mating parts in use and (via various wear/corrosion regimes) everything will knacker itself.

BTW the least likely part to actually wear is the ID of the bearings; the spindle and the top hats always wear first

cheers

[Gattonero]

plenty of HT-II cranksets use an aluminium spindle. In the photos it looks more like an aluminium spindle than a steel one, but photos are deceptive which is why I asked. If it is steel it will be thin walled, go rusty where the plating wears off, and a magnet will stick to it. Aluminium ones go black where they corrode, then get worn smooth where they move around. They are thicker walled and a magnet won't stick.

Strictly speaking what you see there arguably cannot be 'fretting' because this wear mechanism relies upon micro-welding between metals. A tightly fitting plastic sleeve cannot fret, not to start with. It can cause crevice corrosion, it can wear via abrasive wear, there are many possibilities, but not fretting per se.

cheers

Definitively steel. I can tell by looking and feeling the real thing rather than the photos and yes, magnets do stick to it. Memo to self; must use more grease.

Right now, the alloy spindle is used only in the lower class of HT2 cranksets. Say anything that is lower than 105 or Deore, IIRC?
Pretty easy to spot by the thickness, the alluminium one is amost 3mm thick, the steel one just over 1mm. The steel spindle often gets superficial corrosion though this does not gives structural problems.
Both the types can get marks from stuck/rusty bearings that don't spin well, thus making the plastic cover/shim ("top hat") spinning on the alxe rather than spin with the axle. The steel spindle needs quite some abuse to get significant marks, the alluminium one can be damaged easier

[fausto99]

Pictures of the old cleaned up bearings below don't seem to show any significant difference between the drive non-drive side.


non-drive side

drive side


However, there clearly has been rotation of the shaft with respect to the inner of the non-drive side bearing; the shaft is polished where there are no black marks. So, why do Shimano use (soft) plastic on the i.d. of the bearings? Why not something grippier? Why has the same thing not happened on the chainwheel side? How does this occur? I could understand if the bearing was dirty or seized, but if it is still rotating freely why would the shaft rotate in the plastic, in preference to the bearing itself?

As I do not possess inside and outside micrometers and it would be difficult to get to the chainwheel side, I have measured as best I can with digital calipers. I have also tried test fitting of new and old bearings to the shaft. The shaft is at most 1 thou smaller id on the non-drive side compared to the drive side. The shaft is more like 5 thou smaller od for the whole of the middle portion. I can't feel any play on the drive side. I can feel play on the non-drive side which is slightly worse with the old bearing.

I think it would be wastful to scrap the crankset which has such little measurable wear. My current plan would be to use new bearings and dribble in some Loctite 222 into the non-drive side just before the final preload and assembly.

[Airsporter1st]

Pictures of the old cleaned up bearings below don't seem to show any significant difference between the drive non-drive side.


non-drive side

drive side


However, there clearly has been rotation of the shaft with respect to the inner of the non-drive side bearing; the shaft is polished where there are no black marks. So, why do Shimano use (soft) plastic on the i.d. of the bearings? Why not something grippier? Why has the same thing not happened on the chainwheel side? How does this occur? I could understand if the bearing was dirty or seized, but if it is still rotating freely why would the shaft rotate in the plastic, in preference to the bearing itself?

As I do not possess inside and outside micrometers and it would be difficult to get to the chainwheel side, I have measured as best I can with digital calipers. I have also tried test fitting of new and old bearings to the shaft. The shaft is at most 1 thou smaller id on the non-drive side compared to the drive side. The shaft is more like 5 thou smaller od for the whole of the middle portion. I can't feel any play on the drive side. I can feel play on the non-drive side which is slightly worse with the old bearing.

I think it would be wastful to scrap the crankset which has such little measurable wear. My current plan would be to use new bearings and dribble in some Loctite 222 into the non-drive side just before the final preload and assembly.

Loctite 222 is only threadlocker, I believe. They do make a proper bearing fitting compound, Loctite 641, which would be preferable.

[fausto99]

Like this? http://www.bearing-king.co.uk/bearing/l ... -10ml/3818

[Brucey]

IIRC the main difference between various different grades of Loctite (for different applications) is often how viscous it is before it goes off. This controls whether it runs out of the interface before it cures or not.

BTW if you want to assemble the parts with threadlock on the LHS, there is something to be said for installing the RH bearing and the RH crank, then adding the threadlock to the spindle, and then installing the LH bearing over the spindle.

If you try to push the spindle through a coated LH bearing instead, I doubt there will be much threadlock left where it is needed.

cheers

[Gattonero]

.. My current plan would be to use new bearings and dribble in some Loctite 222 into the non-drive side just before the final preload and assembly.

My take is that the plastic bearing covers are to avoid noise and correct tolerances, better a fraction slack than a fraction too tight: the latter will compress the bearings radially after having displaced the inner&outer race while the spindle is fitted.

As long as you do use some quality, sticky grease, you'll be fine the wear is not going to give any structural problem or play that will be felt. Again, bearings don;t like being tight and you ought to have that tiny fraction of slack rather than having them slightly crushed.

The Loctite 222 is a threadlocker with low breaking strength, IIRC in the region of 6Nm at best. The gap-filling is modest too.
You want a proper retaining compound with higher strength, the 641 is ok but the 638 is higher strength (shear strenght up to 4000psi IIRC) so suits better the application as long as you're not planning to remove the cranks frequently: it's likely that while removing the spindle you'll get the Rh bearing cover coming out, too. In such case, the 641 could be better.

[Brucey]

I do not agree that a little slack is better than a little loose in this case. A little slack is exactly what has contributed to the damage that has thus far arisen, and unless you do something now it will only get worse.

Once there is a small clearance present, grease in the interface won't help in any way whatsoever.

cheers

[Gattonero]

If the fitting was too tight you will have either the bearing cover cracked, or the inner race misplaced with the outer race of the bearings, because of the axial force required to "hammer" the spindle in.
It is a slip-fit, not an interference one so there has to be that little amount of slack, which is a very small fraction of mm.

That abnormal and uneven wear is mostly caused by bearing cups not parallel.

[fausto99]

Many thanks for all your thoughts and recommendations. I will certainly look at putting the LHS bearing on last and have a closer look at the various Loctite types and grades.

I'm inclined to agree with Brucey that "slightly loose" is how I ended up with this problem. As I said before, it's the (ball) bearings that should turn, not the plastic plain bush on a steel shaft. If I wanted a plain bearing, I'd use oilite and arrange for a drip feed of oil.